Aquarium filters are essential for keeping pet fish. They keep the water clean, clear, and safe for fish and other aquatic pets. They’re also very affordable and save you doing daily tank cleaning and water changes, therefore they’re one of the main requirements of a home fish owner.
Without a filter, your fish and invertebrates are at risk of oxygen depletion and ammonia poisoning which can kill them in a matter of days or even hours.
There are, however, some aquatic pets that are tougher than others when it comes to surviving less-than-perfect conditions. If you have a power outage or some other emergency, here is a list of types of fish and invertebrates that will survive longer than others without a filter.
- Scientific Name: Betta splendens
- Adult Size: 3 inches
- Life Expectancy: 2 to 3 years
The infamous betta fish or Siamese fighting fish is sometimes listed as a species that can live without a filter. But while a betta may be able to survive in a tank or bowl without a filter for a short time, it definitely won’t thrive.
Sadly, bettas kept in poor water conditions will often die before their first birthday, which is very sad for a beautiful fish that can exceed 5 years in a well-maintained aquarium!
The reason that betta fish are hardier than most is the adaptations they’ve made to their natural habitat. In the wild, bettas are found in shallow pools, swamps, and rice paddies, which can become low in oxygen. To survive such conditions, the beautiful betta has evolved a special organ known as the labyrinth organ which allows them to breathe some of their oxygen from the air as well as the water.
As we’ve said, this mustn’t be taken as a reason to keep bettas in poor water conditions, and their sensitivity to ammonia and other toxins means that a filter is still essential except in emergency situations!
- Scientific Name: Poecilia reticulata
- Adult Size: 2 inches
- Life Expectancy: 2 to 3 years
The poor guppy is the victim of a lot of mistreatment in the pet trade, partly owing to their prolific rate of breeding and the very cheap price you pay for them – people might see them as expendable. But we must remember that the guppy is a popular fish species like any other. If you can become sentimental about your favorite oscar or angelfish, then why not your guppy?!
Guppies are hardy fish that can tolerate an extraordinary range of temperatures, but their tolerance for poor water conditions might not be as endless as you imagine. Guppies are active fish that require decent oxygen levels and can suffer ammonia poisoning just like any other species.
So, remember, they’re likely to survive longer than some other fish, but you’ll still need to change your water often to keep them alive and well.
- Scientific Name: Carassius auratus
- Adult Size: 12 to 14 inches
- Life Expectancy: 15 to 20 years
The goldfish is another fish that often suffers because of its robust reputation. But just because goldfish have been kept in bowls without a filter, doesn’t mean they’re happiest that way.
Goldfish are actually heavy feeders and produce a high bio load, meaning that if you keep them without a filter, you’ll need to change half of their water every day!
While some sources have listed goldfish as a labyrinth fish that can breathe oxygen from the air, this is not true! Like most fish, goldfish can only breathe oxygen that’s been dissolved in the water through their gills.
The real reason that goldfish are good at surviving low oxygen levels is their physical adaptation to suppress metabolism when exposed to poor water conditions.
Funnily enough, the primary organ that they sacrifice to save oxygen is their brain! Maybe it’s why goldfish famously fail the memory test.
- Scientific Name: Corydoras
- Adult Size: 2-3 inches
- Life Expectancy: 5 to 10 years
Corydoras catfish, affectionately known as ‘corys’, are a popular family of catfish for freshwater aquariums. Popular species include the Bronze cory, Panda cory, and pygmy cory.
These bottom feeders do a fantastic job of keeping the tank clean by constantly rooting around in the substrate, looking for algae and food that would otherwise rot and pollute the tank.
In this way, corys do you a favor by supplementing the work of an aquarium filter. But can corys live for long without a filter?
Like betta fish, cory catfish have specialized breathing apparatus that allows them to breathe oxygen from the air as well as water. If you’ve ever seen your cory hurtling towards the surface to gulp a breath of air, before zooming back down to the bottom again, it might mean your tank was low in oxygen.
When my peppered corydoras used to do this, he’d make me laugh – they always look like they’re in such a hurry. I didn’t realize until later that the speed at which they jet to the surface and back again is a behavioral adaptation to keep them safe. Swimming to the surface can be dangerous for such a small catfish, so they need to do it as quickly as possible to avoid being eaten by a larger fish!
- Scientific Name: Helostomatidae
- Adult Size: 3-12 inches
- Life Expectancy: 5-25 years
Gouramis are a popular family of tropical fish that hails from India and China, and all the way down to Indonesia.
Popular species include the Dwarf gourami, Pearl gourami, and Moonlight gourami. Like betta fish, gouramis are labyrinth fish, meaning they can breathe oxygen from the air as well as water.
This gives them a real advantage when living in low-oxygen environments, like the shallow pools that they come from in Asia. Because of this remarkable adaptation, gouramis might live longer than some other fish without a filter.
Gouramis shouldn’t be neglected though, and in the long term will need a filter. In fact, if you take good care of your aquarium water quality and feeding regime, some gourami species can live for more than 20 years!
- Scientific Name: Danio rerio
- Adult Size: 2 inches
- Life Expectancy: 5 years
When we’re looking at hardy aquarium fish species, Zebra danios or the ‘zebra fish’ is about as tough as they come. This fish can tolerate an astonishing range of temperatures, right the way from 45°F – 118°F, which is pretty exceptional for any fish species.
This means Zebra danios are quite comfortable living without a heater, but for how long can they live without a filter?
These small fish are easy to care for and don’t create much of a bio-load, so won’t dirty their water or create a lot of ammonia in a short space of time. They are, however, very active fish and need a plentiful oxygen supply to keep them healthy.
If you somehow find yourself without a filter, be sure to make partial water changes daily to keep your zebra fish alive and well-oxygenated.
- Scientific Name: Macropodus opercularis
- Adult Size: 4 inches
- Life Expectancy: 6 to 8 years
Like gouramis and bettas, paradise fish are part of the Anabantoidei family that possess a labyrinth organ. This means that like its cousins, the paradise fish possesses the superpower to breathe oxygen from the air as well as the water.
Paradise fish were one of the first exotic fish to be imported to Europe for the aquarium trade, and they made a good choice for a couple of reasons: they’re very beautiful and relatively hardy.
Paradise fish can tolerate a wider range of water conditions than many other fish. They’re not too fussy about water pH or hardness, and can even tolerate temperatures down to 65 Fahrenheit.
Their hardiness means you could keep a paradise fish successfully without a heater, and their ability to breathe air might also help them survive longer than other fish without a filter. Just like other fish, however, ammonia would quickly become a problem unless you changed the water every day.
Japanese Rice Fish
- Scientific Name: Oryzias latipes
- Adult Size: 1.5 inches
- Life Expectancy: 3-4 years
Japanese rice fish are energetic little critters that love to zoom around the aquarium night and day. Being from Japan, they’re more cold-hardy than fish species from more tropical regions and prefer to be kept in cold-water aquariums.
The name ‘rice fish’ also tells us exactly where this fish likes to live in their native lands! Like betta fish and gouramis, Japanese rice fish like to hang out among rice paddies, which are essentially fields of rice that are temporarily flooded with shallow water.
These conditions in the rice paddies are quite challenging for fish, with the water being rather cloudy and low in oxygen. So if a fish can survive there, they’ll likely be able to live without a filter for a longer time than fish that come from crystal clear waters.
Cold water is also naturally richer in oxygen than warm water, which can help cold water fish live without additional oxygen for longer periods of time than some tropical fish.
- Scientific Name: Caridea
- Adult Size: 1 – 10 inches
- Life Expectancy: 1-12 years
Aquarium shrimps such as ghost shrimps, cherry shrimps, and Amano shrimps are some of the easiest aquatic pets to keep. They’re normally peaceful, undemanding, and easygoing characters, and also do an excellent job at helping to keep your fish tank clean.
Some people have tried keeping shrimps in a planted fish bowl without a filter, and for a short time, it might work ok.
For the long term, however, keeping shrimp without a filter is not such a good idea. Just like fish, shrimp need a plentiful supply of oxygen, and without it, you might see them dashing to the surface to breathe from the surface layer of water. If you fail to replenish their oxygen supplies when they give you this sign, they’ll likely soon die.
Shrimp are also sensitive to nitrite and ammonia, which will build up in their tank or bowl without a filter. Either way, without a filter you’d need to provide your shrimps with daily water changes to ensure enough oxygen and safe water conditions.
- Scientific Name: Lymnaea stagnalis
- Adult Size: 0.5 inches
- Life Expectancy: 1-2 years
Pond snails are one of the few invertebrates that you might be able to keep in water with low oxygen levels. While most aquatic snails have gills and breathe underwater, pond snails have a primitive lung that allows them to breathe from the air.
This adaptation means that these snails can survive in water that’s very low in oxygen, which, in some circumstances, could help them survive without a filter.
These snails, however, are still sensitive to ammonia spikes and are even used by scientists as a bioindicator for water that’s contaminated. If they’re present and unharmed it means ammonia levels are not excessively high.
On the plus side, pond snails are excellent at keeping your tank clean, and assist your filter in its work of improving water quality.
Pond snails don’t tend to eat healthy live plants, but they can reproduce very quickly, meaning population explosions can be a problem.
- Scientific Name: Planorbidae
- Adult Size: 0.5 – 2 inches
- Life Expectancy: 1-2 years
Like pond snails, Ramshorn snails have a primitive lung, rather than gills for breathing, so can do well in tanks with low levels of dissolved oxygen.
But although these snails have beautiful, spiraling shells, they can also be a pest in the aquarium by devouring your precious live plants as well as the algae and detritus that you want them to eat!
They can also breed very fast, so if you have living plants, it’s best to steer clear of these types of snails.
If you’re not planning on growing plants, however, the Ramshorn snail can be one of the hardiest of aquatic pets you can imagine. Along with the pond snail, they could probably live in water without a filter longer than just about any other aquatic pet you could find.
4 Reasons Aquarium Filters Are Essential
In this article, we’ve listed some of the species of fish and invertebrates that could survive without an aquarium filter for longer than most. But that doesn’t mean they’d be happy or healthy without one.
Aquarium filters perform many crucial roles in a fish tank, and here are a few of the reasons that it’s important to have one:
Filters Oxygenate the Water
All animals, including fish, shrimp, amphibians, and snails need oxygen. While a few of these aquatic pets have a special ability to also breathe oxygen from the air, they’ll be happier if there’s plenty of dissolved oxygen in the water too.
Filters improve oxygen levels by creating a current that improves gas exchange at the water’s surface. The more that the surface water is moving, the more gas exchange can take place, and the more oxygen can be dissolved into the water.
Filters also remove rotting debris from the water which would otherwise consume a lot of oxygen through the process of decomposition.
Filters Remove Toxic Ammonia
Ammonia is one of the most toxic substances to fish, and it just so happens that it’s also what they excrete in their feces.
This means that if fish are kept in a captive environment without a filter or water changes, ammonia levels will quickly build up and cause permanent damage or death to your fish.
Filters remove ammonia from the water by a remarkable process known as “biological filtration.” To put it simply, good bacteria colonize the filter’s media and convert toxic ammonia into less harmful nitrates. This is why every aquarium needs to go through an initiation process known as ‘cycling’ while the beneficial bacteria populations build up enough to do their job properly before fish can be safely introduced.
Filters Save You a Lot of Time and Energy!
If you thought you could save yourself time by not having a filter, think again!
While you’ll only need to clean your filter’s sponges every two weeks or so, an aquarium without a filter will need to be manually cleaned every day!
If you neglected to do this daily cleaning and partial water changes, levels of ammonia would build up, oxygen levels would go down, and your fish would be at great risk of permanent damage or death.
Filters Are Extremely Affordable
The final reason we’ll give to persuade you to get a filter is that they’re very cheap. While advanced canister filters could set you back several hundred dollars, a simple sponge filter with an air pump can be acquired for less than 20 bucks. Not much considering all the work they do for you!
Filters also are quite economical to run, sometimes consuming as little as 5 watts of electricity. This amounts to only around $10 per year!
If You Want To Save Money, Ditch Your Heater Before Your Filter!
If you’re looking to cut your spending costs on keeping fish, then consider a tank without an aquarium heater before cutting out your filter. Heaters cost more money to run than filters. Even a small one for a 10-gallon tank will consume 25 watts – that’s much more than a filter does.
Cold water fish tanks can still be interesting and beautiful, with a wide variety of plants and fish species suitable.
Just looking at the list above, we can find goldfish, guppies, Zebra danios, paradise fish, and Japanese rice fish, all as suitable options for an aquarium without a heater.
Java fern, Java moss, various Anubias, and moss balls are all good plants for an unheated tank too.
To check out our 101-guide for aquarium filters, click here.